Cylinder head and liner hold-down assemblies



Nov. 14, 1961 L. w. STAHL ETAL CYLINDER HEAD AND LINER HOLD-DOWN ASSEMBLIES Filed Nov. 15, 1957 2 Sheets-Sheet 1 Nov. 14, 1961 1.. w. STAHL ET AL 3,008,429

CYLINDER HEAD AND LINER HOLD-DOWN ASSEMBLIES Filed Nov. 15, 1957 2 Sheets-Sheet 2 Leshe W. Jza/z/ f///J W////ams Jr. INYENTO 5 BY i' 6/ ATTO/PAEKS ment has several disadvantages.

United States 3,008,429 Patented Nov. '14, 1 961 3,608,429 a CYLINDER HEAD AND LINER HOLD- DOWN ASSEMBLIES Leslie W. Stahl, Atchison, Kans., and Ellis Williams, .Ir., Beaumont, Tern, assiguors, by mesne assignments, to Dresser Industries, Inc., Dallas, Tern, a corporation of Delaware Filed Nov. 15, 1957, Ser. No. 696,680

19 Claims. (Cl. 103-216) This invention relates to an improved fluidend assembly for a piston type pump and particularly to improvements in a cylinder head and liner hold-down structure. In one of its aspects, it relates to a quick-removable cylinder head. In another aspect, it relates' to a hydraulic hold-down for a cylinder liner.

In piston-type pumps, such as oil well slush pumps, it is customary to providea removable cylinder liner in which the piston reciprocates. This liner, due to pressure diiferentials and the frictional resistance of the piston reciprocating therein, is subjected to considerable force tending to'oause it to reciprocate or breathe. One of the major problems in this art has been to provide a liner hold-down arrangement which is simple in construction and yet will reduce or preferably eliminate breathing of the liner. There have been two principal arrangements used in the past to hold the liner in place. In the first, the cylinder head is bolted to the pump body by a circle of studs and a central stud or studs extend through the cylinder head to be tightened to apply force to the liner via a cage. In the other arrangement, the central stud or studs are eliminated and an extension of 2v out having to generate liner hold-down forces whereby only relatively small force is required to make up such connection.

Another object is to provide a cylinder head liner holddown arrangement in which the cylinder head is threaded into the pump body thereby permitting its quick and easy mounting and demountin'gand in which the liner is held in place by a hydraulic means permitting, if desired, the application of a liner hold-down force of greater magnitude than could be applied simply by tightening the threaded connection between the'cylinder head and pump body.

Another object is to provide such a threaded cylinder head in combination with a liner hold-down means arranged so that force need not be appliedto the liner while the cylinder head is being screwed into or out of position whereby such screw connection can be easily made or unmade.

Another object is to utilize hydraulic pressure continuously to maintain a cylinder liner in a fixed position.

Another object is to provide means for relieving the hydraulic pressure of a cylinder liner hold-down structhe cylinder head bears against the cage so that when a the circle of studs is tightened to hold the cylinder head in place, force is transmitted through the cage to hold the liner in place also. Neither of these arrangements has been entirely successful in preventing liner breath- 'of them more than is necessary, and usually all that he physically can, thereby frequently resulting in unduly stressing the cylinder head and studs.

It is accordingly one object of this invention to provide a liner hold-down arrangement which does not require the tightening of studs to generate the force necessary to hold the liner in place.

As indicated above,xthe cylinder head is customarily held in place by .a circle of studs. Such an arrange- First, it is a timeconsuming and laborious task to remove and replace the cylinder head each time it is desired tosecure access to the pump interior, such as to change the cylinder liner, etc. Secondly, there are usually a large number of studs each of which must be individually tightened,

and, accordingly, there is the distinct probability that they to provide a cylinder head which can be very quickly connected and disconnected from the pump body, in combination with means which can easily be made to hold the liner in place, all without the use of studs or the like,

the arrangement being such thatthe connection between the cylinder head and pump body can be made up with- FIGS. 2 and 3 arrangement; and

ture to facilitate mechanical detachment of the hold-down structure from the cylinder.

Another object is to provide means for automatically modulating the hydraulic pressure applied to the holddown structure so that it will vary with pump pressure thereby assuring sufficient force is always applied to the liner to prevent it from breathing and to maintain its seal with the pump body despite fluctuations in the pump discharge pressure. v

Other objects, advantages and features will be apparent to one skilled in the-art upon studying the specifications, claims and drawings, wherein:

FIG. 1 is a diagrammatic view of a portion of a slush pump to which an embodiment of the invention is appiled; r

FIG. 2 is a horizontal cross-section of the front end of a pump cylinder showing a cylinder head and liner hold-down structure embodying features of the invention;

FIG. 3 is a cross-sectional elevation of a part of the structure useful for automatic modulation of the holddown hydraulic pressure;

FIG. 4 illustrates an alternative embodiment of the FIG. 5 is a view similar to FIG. 2 but showing an alternative cylinder head arrangement and one particularly suited for conversion of existing pumps.

Referring now to FIG. 2, pump cylinder 10 has a liner 11 mounted therein in a conventional manner. Thus the cylinder bore 10a has a shoulder or abutment 12 disposed to oppose a shoulder 13 defined by annular flange 14 on the cylinder liner. Similarly a shoulder 15 on the liner is opposed by end 16 of cage or spacer 17.

Arranged between these respective pairs of shoulders are seals 18 and 19 which, in accordance with conventional practice, can be of the mechanical compression 'or gasket type. This type of seal, of course, requires a unit pressure applied thereto which is greater than the fluid pressure being sealed against.

While a particular liner and seal arrangement has been illustrated, it will be appreciated that it can take other forms, the principal requirement being," insofar as this invention is concerned, that an abutment be provided on the pump against which the liner is to be held.

Cage 17 has ports '26 through which liquid flows to and from'the cylinder liner under the action of piston 21. Other configurations of the cage are possible as long as the cage is formed to transmit mechanical force to the liner to hold it in place and also affords liquid flow to and from the cylinder liner.

In accordance with a preferred embodimentyof this invention, the cylinder head 22 is threaded into bore a of the cylinder, as by threads 23. Preferably, a sliding seal is provided between the cylinder head and cylinder 19 in such a manner as to prevent leakage past the threads. Thus, seal 24 can be arranged on a cylindrical extension 25 of the cylinder head to effect a seal with bore portion 26 of the cylinder. Seal 24 is preferably of the fluid pressure enrgized type, such as an O-ring or a double lip ring positioned with the lips lying respectively against the cylinder head and the cylinder bore and extending toward the interior of the pump to prevent liquid from flowing from the interior to the exterior. The seal will, of course, be of such size that it forms an initial seal between the cylinder bore and cylinder head upon screwing the latter in place. Since it is exposed to internal fluid pressure, it is urged thereby to form a tighter seal as the pressure increases.

With the cylinder head thus arranged, it will be seen that it can be very easily and quickly screwed into place and when in place, seal 24 will prevent leakage from past the cylinder head. As will be more fully pointed out, the cylinder head is normally screwed into and out of position after fluid pressure acting against it has been relieved. Accordingly, the only torque which need to be applied to connect or disconnect the cylinder head is that required to make up the single threaded connection. Also, since a fluid pressure energized seal is preferably used, the connection need not supply any significant force for perfecting the seal as it would if a gasket or mechanical compression type seal were used.

Means are provided for utilizing the pressure of a hydraulic liquid to hold the liner in place and are arranged so that the hydraulic pressure can be applied after the cylinder head has been fastened in place and can be removed before the head is to be removed. This means comprises a pressure responsive member having a force transmitting connection with the liner so that upon application of fluid pressure to the member, a force is generated to hold the liner in place. In the illustrated structure, an intermediate head, shown as a piston 27, and which also can be termed an intermediate head member, is mounted for reciprocation in cylinder 26 With a sliding seal 27a therebetween. Here again a fluid pressure energized seal similar to seal 24 is used and it can be of the types mentioned as examples with respect to the latter seal. While piston 27 is shown to be integrally formed as a part of cage 17, it can be separate therefrom and merely abut against the cage or other means provided to transmit force to the liner. The integral construction will usually be preferred because it reduced the number of parts and permits of easier and more exact assembly.

With this construction it will be seen that the cylinder head, the cylinder bore and piston 27 together define a hydraulic pressure chamber 28 therebetween. Hydraulic fluid such as grease, oil, water, or even the liquid being pumped can be forced by a suitable arrangement, such as a pump, into this chamber to thereby act across the entire cross-section of piston 27 to generate a force which is applied to the liner via cage 17. For example, the hydraulic fluid can be manually pumped, as through conduit 29, into the chamber until the pressure therein is sufficient to satisfactorily hold the liner in place.

The magnitude of this pressure will depend upon a number of factors including the pump discharge pressure, the nature of seals 18 and 19 as well as the forces exerted on liner 11 tending to cause it to breathe, and upon the cross-sectional area of piston 27. When seals 18 and 19 are of the mechanical compression or gasket type, the unit pressure applied thereto must exceed the fluid pressure being sealed against. Accordingly, the hydraulic pressure must be great enough to accomplish this result and will usually be of even greater magnitude in order to prevent breathing of the liner. In any case, the desired pressure can be applied and by proper structural design liner hold-down forces of very large magnitudes can be obtained.

The hydraulic fluid pressure can be developed to a constant value in excess of that expected to be required at the anticipated maximum pump discharge pressure. The hydraulic fluid can then be locked between the two heads as by closing a valve (not shown) in conduit 29. Another simple way of supplying such constant pressure is to substitute conduit 29 with a grease fitting and then to use a grease gun or pump to force grease into chamber 28 until the desired value is achieved. In this arrangement, the pressure of the grease can be relieved as by providing a discharge or manually operable relief valve communicating through cylinder head extension 25 with chamber 28.

In connection with the above, it will be noted that cylinder bore portion 26 is approximately the same diameter (or it can be larger) as bore 10a where the liner is situated. This permits removal of the cylinder liner. Also, with the arrangement as shown in FIG. 2, the pressure in chamber 28 should exceed the pump discharge pressure by an amount required to generate the desired liner hold-down force.

It is further a feature of this invention that the hydraulic pressure applied to chamber 28 is supplied in such a way that it varies in accordance with the pump discharge pressure and yet is always in excess thereof. Such an arrangement is illustrated in FIG. 1 where piston pump 1 is shown as a slush pump having a conventional discharge manifold 30' and a discharge pipe 31. The pump, it will be understood, is equipped with liner hold-down structure similar to that shown in FIG. 2. The discharge pressure is sensed by conduit 32 which applies this pressure to the input of relay 33. The output of the relay has a manifold 34- from which conduits 29 transmit the common pressure to each of the chambers 28 of the hydraulic hold-down structures.

It will be understood that individual relays can be employed for each liner hold-down if such is found to be more convenient.

Referring to FIG. 3, one form of relay for supplying the requisite fluid pressure to conduit 29 has been illustrated as a multiplying relay. The relay structure 33 is characterized by casing 35 in which a piston 36 and a piston 37 are joined together by a rod 38. Piston 37 is of predetermined greater effective cross-sectional area than piston 36. With the cylinder space 39, conduit 29 and chamber 28 filled with liquid, pressures applied to the face of piston 37 will be, in effect, multiplied into pressures on the face of piston 36. With conduit 32 bringing the pressure of manifold 30 to the face of piston 37, pressures will be developed in conduit 29, from the face of piston 36, which are greater than the output pressure of the pump. Therefore, step-up relay 33 is a means through which the discharge pressure of the pump develops pressure which is of a predetermined larger magnitude than the pump discharge pressure. Placing this developed pressure in conduit 29, and therefore, between heads 25 and 27, results in immobilization of liner 11 and prevention of fluid leaking from the cylinder 10.

There are several advantages to be realized in controlling the hydraulic hold-down pressure by the pump pressure as compared with simply fixing it as some constant value as above-described. For example, the pressure in chamber 28 between thetwo heads will automatically increase should the pump discharge pressure increase to an unexpectedly high value. Also the hydraulic pressure will vary with the pump pressure thereby avoiding the necessity for constantly maintaining a pressure in chamber 28 which is the maximum anticipated to be required during peak pump discharge prmsures. Such variation in hydraulic pressure tends to keep a more or less constant differential across seal 27a and a lower average dilferential across seal 24 thereby extending the life of these seals. Further, when the pump is shut down and its discharge pressure falls to zero, the pressure in chamber 28 likewise can fall to zero thereby reducing the likelihood of leakage of hydraulic fluid from the system. Still further it reduces the human factor from the system. As indicated above, a pump mechanic has a tendency to over-apply force to hold a liner in place just to be sure. In this system, he cannot do so because the designer fixes the pressure multiplication factor and the pump itself fixes the absolute liner hold-down force in accordance with its discharge pressure.

It is possible to eliminate the pressure multiplying relay of FIG. 3 and incorporate its function into structure placed in the cylinder head itself. Thus, as shown in FIG. 4, the cylinder head end of the pump has been enlarged and bore 26a therein made of larger diameter than bore a in which cylinder liner 11 resides. Thus, in effect, the cylinder head end is provided with stepped bores 26a and 26. A pressure responsive member shown in the form of a piston 37a has a sliding seal in bore 26a and is connected to piston 27. In FIG. 4, pistons.

37a and 27 are shown to be integral although they can be made separate and provided with a force transmitting connection therebetween. Piston 37a is provided with a seal 37b which preferably is of a fluid energized type as described with reference to seal 24 above.

Means are provided for maintaining the space 41 between seals 37a and 26 and within bore 26a at a relatively low pressure, such as by venting to atmosphere via passage 42. Thus it can be seen there is provided a pressure responsive member such as piston 37a for generating a liner hold-down force under the influence of pressure in chamber 43. To permit this, means are pro vided for maintaining at least a portion of the other side of this member 37a at a lower pressure so that a differential pressure can be developed across it. Such means is here shown as including the smaller diameter piston 27 and vent passage 42. I

With this arrangement, it will be seen that any pressure applied via conduit 29 to chamber 43 will generate a larger liner hold-down force than would the same-pres sure applied to chamber 28in FIG. 2. In a preferred form, the pressure applied via conduit 29 will be the pump discharge pressure. The net liner hold-down force will then be equal to this pressure multiplied by the annular area of pistons 2737w lying between seals 26 37b. Of course, pressures other than pump discharge pressure can be used such as, for example, one applied from an external pump, a grease gun or the like.

FIG. 5 illustrates an alternative embodiment of FIG. 2. In the latter, the threads for holding the cylinder heads in place are cut in the pump cylinder itself. While such an operation could possibly be done in the field, such is usually diflicult and it is more convenient to do it in a central shop. To facilitate the field conversion of existing pumps to the practice of this invention, the threads for the cylinder head are cut in a separate annular ring or flange 44 as shown in FIG. 5. This ring or flange has a stud circle drilled to match that of existing pumps so that the ring or flange can be bolted into place by studs 45. Cage 17, piston 27 and cylinder head 25 can then be placed in operating position as described with reference to FIG. 2. In other respects, the construction and operation of the FIG. 5 arrangement is the same as that in FIG. 2.

It is contemplated that the above pressure multiplying arrangements can be supplied with fluid pressure from any suitable source although pump discharge pressure is preferred.

From the foregoing, it can be seen that after the liner and cage have been inserted, the cylinder head can easily be screwed into place. To facilitate this bar holes 22a can be provided to receive a bar for spinning the cylinder head in place. The threaded connection 23 need be taken up enough only to assure that the cylinder head will not jar loose during operation of the pump. No torque need be applied to create a liner holding force nor, when the preferred seals are used, to tighten against a gasket type seal. Then conduit 29, or a grease nipple, can be connected as shown in order to apply pressure to create the liner hold-down force. To dismantle the pumps front end, pressure in chamber 28 (or 43) is first relieved. Where the systems of FIGS. '1 or 4 are used, the chamber pressure will automatically fall to zero when the pump is shut down and its discharge pressure reduced to zero. If desired, a charging and relief valve 29a can be used to facilitate charging the system with liquid and also, where required, to bleed down its pressure. Where fluid is injected by a gun or pump, a relief valve such as 29a leading to chamber 28 can be opened to relieve the chamber pressure before the .cylinder head is removed. Of course, the system of FIG. 4 will usually be charged with the pumped fluid and in such case',--a relief valve will be used, if at all, merely to bleed air fromthe system.

In the construction shown, pistons 27 and 37a have a smooth outer face and fit'slidingly in bores 26 and 26a respectively. To facilitate withdrawal of the pistons and cage, a threaded opening 40 is provided and a stud or the like can be screwed into this, after the cylinder head has been removed, in order-that the piston and cage can be removed.

Where the term hydraulic fluid has been used herein as being the medium for pressu rizing chamber 28, it will be understood to encompass any suitable liquid, including greases, and not merely an oil especially prepared for hydraulic purposes. Also, it will be understood that while the invention has found particular use in slush pumps, it is also usefulon acidizing, cementing, and other types of piston pumps.

From the foregoing it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth, together with other advantages which are obvious and which are inherent to the apparatus.

It will be understool that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations; This is contemplated by and is Within the scope of the claims.

As many possible embodiments may be made ofthe invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying dnawings is to be interpreted as illustrative and not in a limiting sense. v

' The invention having been described, what is claimed is:

1. In a piston type pump, a housing providing a pump cylinder, a cylinder head, a threaded connection between the cylinder head and the housing so that the cylinder head closes the outer end of the cylinder and yet can be quickly connected and disconnected from the housing, a liner in the cylinder engaging an abutment therein which limits movement of the liner in a direction away from the cylinder head, said liner being removable through the outer end of the cylinder when the head is disconnected therefrom, a pressure responsive member mounted for reciprocation in the pump cylinder intermediate the liner and cylinder head and, with the latter, defining a variable volume pressure chamber in the cylinder, said member having a connection with the liner on the side of the member opposite said chamber and transmit-ting force from the member to the liner to urge the liner into engagernent with said abutment when said force is acting in a direction toward the liner, and means for introducing pressure fluid into said chamber to act against said member to develop said force, the last mentioned means also permitting the pressure fluid to flow from the chamber when desired to reduce the pressure therein.

2. The pump of claim 1 wherein sliding seal means is provided between said cylinder head and the inner wall of said cylinder, said seal means being of the fluid pressure energized type forming an initial seal between the cylinder and cylinder head upon screwing the latter in place, thereby facilitating mounting and removal of the cylinder head, said seal means being exposed to pressure within said cylinder and urged thereby into tighter sealing engagement.

3. In a piston type pump, a housing providing apump cylinder, a cylinder head, a threaded connection between the cylinder head and the housing so that the cylinder head closes one end of the cylinder and yet can be quickly connected and disconnected from the housing, a liner in the cylinder and adapted to be held in place by the El plication of-an endwise force thereto, said one end of the cylinder being of such size as to permit the liner to be removed therethrough upon disconnection of the head, and means for applying said endwise force including a fluid pressure responsive member disposed in said cylinder between the 'liner and cylinder head and having a connection with the liner on one side of said member for transmitting force from the member to the liner to urge the liner into place when the force is acting in a direction toward the liner, and means for applying fluid pressure to the other side of said member to develop said force.

4. In a piston type pump, a housing providing a pump cylinder, a cylinder head, a threaded connection between the cylinder head and the housing so that the cylinder head closes one end of the cylinder an yet can be quickly connected and disconnected from the housing, a

fluid pressure energized seal between the cylinder head and pump housing arranged so that it forms an initial seal when the cylinder head is screwed into place and being expgsed to fluid pressure in the cylinder and urged thereby into tighter sealing engagement, a liner in the cylinder engaging an abutment on the pump body and removable through said one end of the cylinder when the cylinder head is disconnected therefrom, and fluid pressure responsive means disposed in said cylinder between the liner and cylinder head for holding the liner against said abutment and having a force transmitting connection with the liner so that as fluid pressure is applied to said means to urge the means toward the liner, force is transmitted from the means to said liner in a direction to urge the liner against such abutment.

5. In a piston type pump, a housing providing a pump cylinder, a liner in the cylinder and arranged to bear against an abutment in the housing, a cylinder head, a threaded connection between the cylinder head and the housing so that the cylinder head closes the outer end of the cylinder, a head member intermediate the cylinder head and liner and reciprocally mounted in and slidably sealed in the cylinder and having a force transmitting connection with the cylinder liner, said cylinder head with the intermediate head member defining a variable volume pressure chamber in the cylinder, said outer end of the cylinder being of such size as to permit the liner to be removed therefrom upon removal of the cylinder head therefrom, and means for maintaining a fluid pressure said chamber acting on the intermediate head member to rge such member toward the, cylinder liner to hold the liner against said abutment.

6. The pump of claim 5 wherein said means for maintaining said fluid pressure includes a relay responding to an input fluid pressure and providing an output pressure which is of a predetermined greater value than the input pressure, means connecting the output of the relay to said chamber and means establishing the relay input fluid pressure as the discharge pressure of the pump whereby the pressure in said chamber is always greater than the discharge pressure of said pump.

7. In a piston type pump including a housing providing a pump cylinder, a cylinder head, a threaded connection between the cylinder head and housing so that the cylinder head closes one end of the cylinder and yet can be quickly connected and disconnected from the housing, a liner in the cylinder engaging an abutment therein and being removable through said one end of the cylinder when the head is disconnected from the housing, a piston reciprocally mounted in the cylinder intermediate the liner and cylinder head and, with the latter, defining a variable volume pressure chamber in the cylinder, said piston having a force transmitting connection with the liner so that movement of the piston toward the liner urges the liner into engagement with said abutment, and means controlled by the pump discharge pressure for supplying fluid to said chamber to act on the piston to urge it toward the liner, said means supplying said fluid at a pressure which is greater than said discharge pressure.

8. In the pump of claim 7 wherein said means provides a variable pressure output supplied to said chamber with such output being a predetermined function of said pump discharge pressure.

9. in the pump of claim 7 wherein said means is a pressure multiplying relay having its input connected to the pump discharge and its outlet to said chamber.

10. In a piston type pump, a housing providing a pump cylinder with an internal abutment, a cylinder liner bearing against the abutment, a cylinder head, a threaded connection between the cylinder head and housing so that the cylinder head closes the outer end of the cylinder and yet can be unscrewed from said housing to permit removal of the liner, a piston in the cylinder between the cylinder head and liner and being slidable in the cylinder toward and away from the liner and with the cylinder head defining a variable volume pressure chamber in the cylinder, a spacer between the piston and liner and bearing against each so as to form a force transmitting connection between the piston and liner, and means maintaining fluid pressure in said chamber urging the piston toward the liner so as to thereby apply force via the spacer to the liner to hold it against said abutment.

11. The pump of claim 10 in which the means for maintaining the fluid pressure in the chamber between the piston and cylinder head includes a fluid pressure fitting ha ing a fluid connection with the cylinder head to pass pressure fluid to said chamber and which can be closed off after pressure fluid has been introduced from a source to form a closed system exerting a fluid pressure hold-down force of desired value on the liner as it bears against the cylinder abutment.

12. In a piston type pump, a housing providing a plurality of pump cylinders, a plurality of cylinder heads, threaded connections between the respective cylinder heads and the housing so that each cylinder head closes an outer end of a cylinder, an abutment within each cylinder, a liner in each cylinder, said cylinder head being disconnectable from said housing to permit a liner to be removed from its respective cylinder, a shoulder on each liner bearing against its cylinder abutment, a spacer in each cylinder abutting the liner in that cylinder so that movement of the spacer toward its liner urges such liner against its cylinder abutment, a head in each cylinder intermediate the spacer in such cylinder and the cylinder head for such cylinder and slidably sealed to its cylinder wall and abutting its spacer so that movement of the intermediate head toward its liner urges the latter against its abutment, a relay responding to a common discharge pressure from the pump as an input fluid pressure and producing a plurality of output fluid pressures, wherein each is greater than the input fluid pressure, and means for placing the output fluid pressures respectively between the cylinder heads and intermediate heads of each cylinder to exert a fluid pressure hold-down force on each liner which is greater than the fluid pressure in the cylinder it seals.

13. The pump of claim 12 in which the relay comprises, a casing having two piston cylinders, one of which has a cross-sectional area which is larger than the other, a piston in each cylinder of the casing, a connection between the two pistons, fluid pressure connections through opposite walls of the casing whereby the fluid pressure input to the relay is placed on the face of the larger piston and the fluid pressure output from the relay is developed in the cylinder of the smaller piston.

between the cylinder head and housing so that the cylin- I der head closes one end of the cylinder and yet can be quickly connected and disconnected from the housing,

a liner in the cylinder and adapted to be held in place by the application of an endwise force thereto, said liner being removable through said one end of the cylinder when the head is disconnected from the housing, and means for applying such force including a pressure responsive member mounted for reciprocation in the cylinder intermediate the liner and cylinder head and, with the latter, defining a variable volume pressure chamber in the cylinder, said pressure responsive member having a connection with the liner on one side of said member and transmitting force from the member to the liner to urge the liner into place when the force is acting in a direction toward the liner, means for maintaining a pressure on at least a portion of the side of said pressure responsive member opposite said chamber at a lower value than-the pressure in said chamber, and means for applying pressure to said chamber to develop said force.

15. The pump of claim 14 wherein said pressure responsive member is a first piston and said pressure maintaining means includes a second piston intermediate the first piston and the liner and of a smaller cross-sectional area than the first piston, and means venting the space in the cylinder between said first and second pistons.

16. In a piston type pump having a housing providing a pump cylinder, a cylinder head, a threaded connection between the cylinder head and housing so that the cylinder head closes one end of the cylinder, a liner in the cylinder and adapted to be held in place by an endwise force applied thereto, the one end of the cylinder being of such size as to permit the liner to be removed therefrom upon removal of the cylinder head, first and second pistons having a sliding seal with the cylinder intermediate said cylinder head and liner, the first piston being of larger cross-sectional area than the second piston and being closer to the cylinder head, a vent from the cylinder between said pistons, said pistons and liner having a connection therebetween for transmitting endwise force developed by the first piston to the liner, and means for introducing fluid into the cylinder between the first piston and cylinder head.

17. The pump of claim 16 wherein said means for 1 introducing fluid includes a conduit having communication with the pump discharge to apply pressure therefrom to said chamber.

18. In a piston type pump, a housing providing a pump cylinder, an internally threaded annular flange removably connected to the end of the housing and aligned coaxially therewith, a cylinder head, a threaded connection between the cylinder head and said flange so that the cylinder head can be quickly connected and disconnected from the housing, a liner in the cylinder and adapted to be held in place by the application of an endwise force thereto, said liner being removable through said one end of the cylinder and said annular flange upon disconnection of the head therefrom, and means for applying such force including a pressure responsive member in said cylinder between the cylinder head and liner and having a connection with the liner on one side of said member for transmitting force from the member to the liner to urge the liner into place when the force is acting in a direction toward the liner, and means for applying fluid pressure to the other side of said member.

19. The pump of claim 18 wherein said pressure responsive member is a piston having a sliding seal with the cylinder.

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